Copper (Cu) has a lower resistivity (1.7 μΩ·cm) compared to aluminum (Al) with a resistivity of 2.7 μΩ·cm. Additionally, copper has a higher resistance against electro-migration and stress-migration and has been used as a material for manufacturing an interconnection body in semiconductor devices. Examples of semiconductor devices may include silicon semiconductor devices including large scale integrated (LSI) systems, flash memory devices or the like, or large size liquid crystal display devices (LCD) (for example, refer to patent documents 1 to 3).    [Patent Document 1]: Japanese Unexamined Patent Application Publication No. 2005-277390    [Patent Document 2]: International Publication No. WO2006/025347A1    [Patent Document 3]: International Publication No. WO2007/100125A1
For example, in a silicon LSI system used as a central processing unit (CPU), copper interconnection with damascene structure are used as an interconnection body. In this structure, copper which composes the interconnection body, is formed so as to fill the inside of trenches or via holes provided on an insulating layer made from silicon dioxide (SiO2) or the like (refer to non-patent document 1).    [Non-Patent Document 1] “Semiconductor Device (2nd edition)—Physics and Technology” by S. M. Sze (ISBN4-7828-5550-8 C3055), Oct. 5, 2005, Sangyo Tosho, Co., Ltd., third impression of second edition, P355-356.
In order to prevent the degradation of insulating properties of the insulating layer, due to the atomic diffusion of copper forming the interconnection body into the insulating layer, or on the other hand, to prevent an increase in the electric resistance of the copper interconnection body, due to the atomic diffusion of atoms composing the insulating layer, such as silicon (Si) into the interconnection body, it is common to configure a copper interconnection structure including a barrier layer formed between the insulating layer and the copper interconnection body. This barrier layer may prevent the mutual diffusion of atoms while forming the copper interconnection structure (for example, refer to patent documents 4 to 6).    [Patent Document 4] Japanese Unexamined Patent Application Publication No. H01-202841    [Patent Document 5] Japanese Unexamined Patent Application Publication No. H11-186273    [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2001-44156
Conventionally, the barrier layer of the copper interconnection structure is made from tungsten nitride (WN) (for example, refer to patent document 7), tantalum (Ta) (for example, refer to patent document 8), rhenium (Re) (for example, refer to patent document 9) and the like.    [Patent Publication 7] Japanese Unexamined Patent Application Publication No. 2000-068269    [Patent Document 8] Japanese Unexamined Patent Application Publication No. 2004-266178    [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2007-096241
In recent years, in view of the necessity for decreasing the interconnection width (32 nm or less) to increase the LSI integration density, a technique has been disclosed to form a thin barrier layer. The thin barrier layer is formed from a self forming manganese oxide layer or the like using a copper layer containing an additional element such as manganese (Mn). The additional element of the copper layer has a diffusion coefficient greater than the self diffusion coefficient of copper (refer to patent publications 1 to 3 above).
In order to form a barrier layer using a copper layer containing manganese (Mn), it is common to first deposit a copper alloy layer so as to cover an inner surface of a trench opening provided on an insulating layer. Examples of the insulating layer may include porous silicon dioxide (SiO2), silicon carbide oxide (SiOC) or the like. Second, it is common to bury copper, which forms the interconnection body, into a remaining space of the trench opening or via hole, and then heat treating the copper alloy layer and the copper interconnection body in an atmosphere containing oxygen molecules.
By this heat treatment, a barrier layer containing silicon (Si), oxygen (O), and manganese (Mn) is formed between the insulating layer and the copper interconnection body (for example, refer to patent documents 1 and 2 above). Alternatively, a barrier layer containing silicon (Si), oxygen (O), manganese (Mn), and copper (Cu) may be formed (refer to patent document 3 above). It is also known that an additional barrier layer may also be formed in close proximity to a so-called open surface area, such as an upper surface of the copper interconnection body, where the additional barrier layer is not facing the insulating layer. The additional barrier layer is formed by a reaction with the atmosphere containing oxygen molecules when the heat treatment is applied (for example, refer to patent documents 1 to 3 above).
In the barrier layer, formed between the copper interconnection body and the insulating layer, some requirements, such as an atomic concentration of manganese distribution, has been already known to provide a barrier layer with sufficient barrier properties (refer to patent document 3 above). Meanwhile, it is still unclear what type of internal configuration may exercise effective barrier functions for the barrier layer formed the open surface of the copper interconnection body. In addition, it is further unclear what types of process may be used to form a stable barrier layer, on the open surface of the copper interconnection body, with effective barrier properties.
The present invention is made under the above-mentioned situation. The purpose of the present invention is to provide a copper interconnection structure having an effective barrier function in the barrier layer on the open surface of the copper interconnection body by providing an appropriate internal structure in the barrier layer. Further, the purpose of the present invention is to provide a method for forming the copper interconnection structure including the barrier layer having such an effective barrier function. Further, the purpose of the present invention is to provide a semiconductor device having the copper interconnection structure as a circuit interconnection.